Add another packing test.
Add another packing test.

* subversion/tests/libsvn_fs_fs/fs-pack-test.c
  (pack_even_filesystem): New test which checks packing in the scenario
    where all current shards are full.
  (test_funcs): Add new test as XFail.

jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion